Grassley sent a letter to Comptroller General Gene Dodaro requesting an assessment of the Optional Practical Training program, which allows students from other countries to work in the United States.

"I'm seeking the assistance of the Government Accountability Office (GAO) to fully investigate the use of OPT, including who uses it and how students are tracked, determine what weaknesses exist, and suggest ways to improve the procedures and policies that govern its administration," Grassley writes in the letter sent Thursday.

"I am concerned that the Executive branch has not and is not thoroughly vetting the applications from college and universities, and that it is rarely denying OPT work authorizations," the senator from Iowa continues. "According to data provided by the Department of Homeland Security, USCIS has denied very few applications, rejecting, on average, between 2 and 3 percent of applications submitted."

In the letter, Grassley writes that students in the program could be gaming the system through loopholes that allow them to not work or not work where they claim to be working.

Grassley adds that the program could be causing unfair competition with American workers.

"Also, the increased amount of time that one could work in the United States, without wage requirements or American worker protections, may be undermining other visa programs such as the H-1B visa program," Grassley writes. "It may also be disadvantaging American students who are looking for work during these tough economic times. OPT was meant to be supplementary to one's studies, not as a bridge to an H-1B visa or permanent residency. It should also not be used to allow students to remain in the U.S. until work is available, which creates competition for American students and workers."

Grassley's letter comes as Republicans and Democrats begin to spar over immigration reform through the Democrat backed-DREAM Act and a Republican alternative sponsored by Sen. Marco RubioMarco Antonio RubioRepublicans struggle to save funding for Trump's border wall Rubio: Dropping FARC from terrorist list threatens Colombians, US security This Thanksgiving, skip the political food fights and talk UFOs instead MORE (R-Fla.). Both bills are meant to help young immigrants who are in the country illegally — while the Development, Relief and Education for Alien Minors (DREAM) Act creates a path to citizenship, the Republican alternative proposal does not. On Wednesday Rep. David Rivera (R-Fla.) introduced a similar version to Rubio's bill in the House of Representatives.

Read Grassley's letter below:

Grassley Letter to GAO on OPT